Phone metadata reveals where city migrants go and who they call

Still adjusting to life in the big city? Your mobile phone operator might soon be able to tell.

An analysis of a month’s worth of telecoms metadata – more than 698 million call logs – from Shanghai has given insights into where people live, who they meet and their movements when they first arrive in a new city. The study – using data provided by mobile network China Telecom – could help authorities manage mass migration more effectively in the future, although it might alarm some civil liberty groups.

Although the data didn’t contain names and addresses, it did suggest whether mobile users were locals or migrants to the city. Other biographical information was included, such as sex and age. Some 22,000 “new migrants” were defined as those who were born outside Shanghai and who did not have call logs in the first week of the month, while one million “settled migrants” had at least one call in that time period. There were 1.7 million locals.

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The data covered September 2016, but revealed who called whom and showed roughly where in the city people went, thanks to information on which cell towers they connected to.

Becoming local

Chenhao Tan at the University of Washington in Seattle, who worked on the project with colleagues at Zhejiang University in China, says he was expecting the data to reveal migrants gradually behaving more and more like locals as they spent time in Shanghai.

“That’s actually not the case, they remain quite different from locals,” he says. For instance, the migrants stayed in contact with multiple people who shared their place of birth. They also spent more time in the centre of the city.

However, migrants did become more like locals in some ways – such as average call duration and the distance they travelled. The settled migrants and locals groups were also more likely than newcomers to receive reciprocal calls from people they contacted.

De-anonymising data

“The real value in this work is in the potential of telling us the rate of change in integration of a community over time,” said Rex Douglass at the University of California, San Diego. “Cellphone data provide an opportunity to show how these intercommunal ties grow or evaporate over time in a way that demographic or survey data have a hard time capturing.”

However, the use of mass telecoms metadata is controversial, because it is relatively simple to tie a person’s identity to nominally anonymised information. Civil liberties groups have long worried about the very thing this research suggests: that despite not including names or the content of calls, such data reveal insights about people’s lives.

Tan says that such insights might actually help governments or charitable organisations assist migrants. “Governments may be able to more effectively deliver information on potential benefits,” he says.